The connection_edge_process_relay_cell function in or/relay.c in Tor before 0.2.3.25 maintains circuits even if an unexpected SENDME cell arrives, which might allow remote attackers to cause a denial of service (memory consumption or excessive cell reception rate) or bypass intended flow-control restrictions via a RELAY_COMMAND_SENDME command.
https://trac.torproject.org/projects/tor/ticket/6252
https://gitweb.torproject.org/tor.git/blob/release-0.2.3:/ReleaseNotes
https://gitweb.torproject.org/arma/tor.git/commitdiff/b9b54568c0bb64c32bd0b362954bdbc8c1234b16
https://exchange.xforce.ibmcloud.com/vulnerabilities/80289
https://bugzilla.redhat.com/show_bug.cgi?id=880310
https://bugs.gentoo.org/show_bug.cgi?id=444804
http://security.gentoo.org/glsa/glsa-201301-03.xml